Thomas (1996) undertook
an analysis of the floristic variation in community types within the California
portion of the Mojave Desert to determine how well they could serve as a coarse-filter
for representing plant species in conservation strategies. Using a Jaccard's
similarity coefficient to measure the homogeneity of the CNDDB communities based
on approximately 1150 species in an existing database (Lum 1975), Thomas (1996)
distinguished two subregions of the Mojave (western and eastern­see Figure
MOJ-1) in order to describe systematic geographic variation in floristic composition
in some widespread vegetation types. erefore, separate gap analyses were conducted
in the two floristic divisions. Therefore, separate gap analyses were conducted
in the two floristic divisions.

The Mojave region is characterized
by basin and range topography as illustrated in Figure MOJ-1. The basins often
contain dry lakes or playas. The lowest point in the Mojave and the United States
is -86 meters in the Death Valley basin. Nearby is the highest point in the
Mojave, Telescope Peak, at 3368 meters. Numerous other ranges exist; the highest
being the New York Mountains (2296 m), Kingston Mountains (2232 m), Clark Mountains
(2417 m) and Providence Mountains (2186 m).

Geologically the Mojave
consists of a variety of substrates and geomorphic features. Faults are common,
notable ones being the Garlock Fault and the San Andreas Fault near the southern
boundary of the region. Historic lake beds and volcanoes have left their imprint
on the region in the form of unique landforms and substrate material. A typical
geomorphic sequence that can be observed is the hill or mountain upland eroding
onto bajada or piedmont which slopes down to a dry lake. Soil formation is often
minimal compared to regions with higher vegetation cover and more rain.

The Mojave climate dominates
the rate and direction of many physical and biotic processes in the desert.
Diurnal temperature differences may be extreme (up to 25 °C ; Rowlands
et al. 1982). Heat in the summer is an overriding factor (47°C mean July
maximum at Death Valley; Rowlands et al. 1982). Winter may bring snow or frost.
Rainfall is sparse and highly variable on a seasonal and annual basis (mean
annual of 41 to 136 mm/yr depending upon the weather station; Rowlands et al.
1982). Windstorms contribute to erosional factors and increase the desiccation
rates to which plants and animals must adapt.

Land Stewardship

Over three quarters of
the Mojave is in federal jurisdiction (77%). The three main federal land administrators
are the BLM (34%), National Park Service (28%) and Department of Defense (14%).
The 4 large DoD bases­Edwards Air Force Base, China Lake Naval Weapons
Center, Fort Irwin, and Twentynine Palms Marine Corps Base­were categorized
as status level 3 because much of their lands are unused. The USFS administers
0.3% of the land, primarily along the western edges of the region. The California
Desert Protection Act of 1994 (CDPA) changed the administrative composition
of federal land (14.2% less BLM land and 14.1% more NPS land) and added a small
amount of state land (plus 0.1%). The California Department of State Lands administers
0.2% of the land area, CDF&G 0.1%, and other state lands comprise 2.0%.
Private land, comprising 21% of the Mojave, are mostly located in the western
portion in Antelope Valley and along the southwestern border, including Morongo
and Yucca Valleys. Urbanization has exploded in these areas, with the communities
serving in a sense as extensions of the greater Los Angeles economic center.
Private and state lands occur in a checkerboard pattern embedded in a matrix
of federal properties, a pattern established in the 19th century as a result
of federal policy of land allocation during the homesteading and railroad development
period. The checkerboard pattern of land management has resulted in a situation
where the management levels occur in fragmented matrices; this is particularly
evident across the central Mojave along the Interstate 40 corridor (Figure MOJ-2).

Figure MOJ-2. Management status
of lands in the Mojave Desert Region. See text for definitions of management levels.

As reported for the Sonoran
Desert region in Appendix SON, the wilderness designations and expansions
of National Parks in the California deserts legislated in the CDPA were incorporated
into the final stewardship for CA-GAP. The data were primarily obtained from
a preliminary digital version of the 1991 version of the bill, but excluding
areas that were omitted in the final version of the bill. Some boundaries may
have been adjusted by Congress between these two versions, and thus there may
be small errors in the reported area by management levels and the management
status of plant community types and vertebrate species.

Table MOJ-1. Area and percentage
of land surface by management status level of the Mojave Desert Region of California.
(The table compares management levels before and after the passage of the
California Desert Protection Act of 1994)

Pre-bill
Status

Current
Status

Status

Area
(km²)

%

Area
(km²)

%

1

10,414

14.0

26,851

36.3

2

1,016

1.4

1,747

2.4

3

46,219

62.5

29,149

39.4

4

16,340

22.1

16,242

21.9

Total

73,989

100.0

73,989

100.0

The CDPA increased the
proportion of status 1 lands in the Mojave region by approximately 150%, from
14 to 36% (Table MOJ-1, Figure MOJ-2). Fifty-seven status 1 managed areas were
mapped for the region, including those established by the CDPA. Of these, BLM
manages 41 wilderness areas. There are also 5 USFS wilderness areas, 3 national
park units, 3 TNC preserves, 2 CDF&G ecological reserves, 1 state reserve,
and 2 UC natural reserves. The vast majority of status 1 land area is managed
currently by the NPS, with over 20,000 km², followed by BLM with over 6,000
km², mostly in wilderness areas. Other status 1 areas total less than 100
km² per agency.

The management profiles
of the two floristic subregions are quite different (Table MOJ-2). The majority
of the status 1 managed area is in the eastern subregion, with very little status
4 land. The western Mojave, on the other hand, has a more modest amount of status
1 and 2 land with nearly half in status 3 and a third in status 4. The western
portion is where the military bases and most private ownership occurs in the
Mojave Desert.

Table MOJ-2. Area and percentage
of land surface by management status level of the two floristic subregions of
the Mojave Desert Region of California.

West
Mojave

East
Mojave

Status

Area
(km²)

%

Area
(km²)

%

1

5,074

13.4

21,777

60.5

2

1,594

4.2

153

0.4

3

18,370

48.4

10,763

29.9

4

12,911

34.0

3,329

9.2

Total

37,950

100.0

36,021

100.0

There are 42 status 2 managed
areas within the Mojave Region. The majority (27) are BLM Areas of Critical
Environmental Concern or wilderness planning areas. There is one national wildlife
refuge (Havasu), 7 state wildlife areas, and 2 state parks.

Of the 99 status 1 and
2 managed areas, 35 are larger than 10,000 ha in size (ignoring adjacencies
among areas). Mean size of status 1 areas is 47,100 ha while status 2 is 4,160
ha. The largest are the NPS units, while most of the remainder are newly designated
BLM wilderness areas. At the small end of the scale, 26 areas are less than
1,000 ha, although some of these are small portions of large managed areas from
adjoining regions.

Figure MOJ-3. Comparison of
the proportion of managed areas with all lands in the Mojave Desert Region by
elevation zones.

As with most other regions
in the state, management is not uniform across elevation zones (Figure MOJ-3).
The proportion of status 1 and 2 lands increases steadily with elevation, with
a peak in the 501-1000 m zone. On the other hand, 70% of the lands in the region
are in the 1-500 m zone where only 16% of protected lands occur.

Plant Community Types

The Mojave Region land-cover
database was developed using existing maps as baseline source data, including
the East Mojave Resource Inventory from Southern California Edison, the BLM
West Mojave map (Clark, personal communication), CALVEG (Parker and Matyas 1981),
Edwards Air Force Base, Twentynine Palms Marine Corps Base, Joshua Tree National
Monument (Leary 1977), and a BLM/USGS map derived from MSS imagery. Maps were
updated and refined using Thematic Mapper satellite imagery, a current 1:150,000
road atlas (to identify areas of residential or industrial development), and
extensive reconnaissance level field survey (see Thomas 1996 for details). Seven
expert reviewers made comments on a draft version, and the map was revised accordingly.
The revisions made by the Bureau of Land Management for their Northern and Eastern
Colorado Desert planning area (Dorweiler 1997) included a small part of the
southern Mojave Desert region. The revisions were incorporated into the final
CA-GAP land-cover as described above for the Sonoran Desert region. Because
these existing sources could only reliably determine community types, information
on dominant species was generally not recorded for map units in this region.
While logistics and resources prevented an extensive, quantitative accuracy
assessment, an evaluation was made in the eastern Mojave region using a set
of 462 transects collected for BLM in 1975. Overall accuracy of the map based
on these plots was 84%, with class accuracies ranging from 65-100% (Thomas 1996).
A confidence rating was applied to each map unit and summarized for each cover
type. Cover types with the most questionable reliability are Mojave Mixed Woody
Scrub, Mojave Mixed Steppe, Mojave Mixed Woody and Succulent Scrub, Blackbush
Scrub, Shadscale Scrub, Desert Native Grassland, Transmontane Freshwater Marsh,
Foothill Pine-Oak Woodland, and Bristlecone Pine Forest. Cover types of questionable
reliability occur mainly on lands administered by China Lake Naval Weapons Center
and Death Valley National Park and to some extent Fort Irwin Military Reservation,
Mojave National Preserve, and Joshua Tree National Park.

The Mojave land-cover database
contains distribution information on 33 natural vegetation communities and 8
land use or non-vegetated types. Three new community types were described for
gap analysis­Black Sagebrush Scrub (35213), Desert Holly Scrub (36150),
and Desert Native Grassland (42160). Three vegetation types contribute to 75%
of the land cover in the Mojave region. The most prominent vegetation community
is Mojave Creosote Bush Scrub which contributes 57%. Mojave Mixed Woody Scrub
contributes 13% and Desert Saltbush Scrub contributes 5%.

Not all cover types were
evaluated for protection status. Cover types eliminated were those: 1) with
less than 25 km² total area, 2) cultural and barren in nature, 3) characterized
by non-native or disturbance following species, and 4) widespread outside the
Mojave and not characteristic of the desert. The size constraint was imposed
because the minimum mapping unit employed in gap analysis is not sensitive to
highly localized cover types or extensive types that may occur in small patches.
Also because of differences in cover type definition between the source data,
localized cover types may not be representatively mapped across all source data.

Fifteen (unshaded rows
of Table MOJ-3) of the 33 original vegetated land-cover types were eliminated
from further evaluation. These include 9 cover types with less than 25 km²
distribution: Black Sagebrush Scrub, Bristlecone Pine Forest, Foothill Pine-Oak
Woodland, Desert Greasewood Scrub, Modoc-Great Basin Willow Riparian Forest,
Mojave Desert Wash Scrub, Transmontane Alkali Marsh, Transmontane Freshwater
Marsh, and Wildflower Field. Two cover types characterized by invasive exotic
species, Non-native Grassland and Tamarisk Scrub, were eliminated as was Rabbitbrush
Scrub, a disturbance maintained cover type (Holland 1986). Three cover types
that are extensive outside of the Mojave region were eliminated, those being
Interior Live Oak Chaparral, Chamise Chaparral and Sonoran Creosote Bush Scrub.
The chaparral areal occurrence in the Mojave is relatively small (114 km²
and 57 km² respectively) and may be an artifact of boundary placement between
the Mojave and Southwest regions. Likewise, Sonoran Creosote Bush Scrub with
779 km² is more extensive in the Sonoran region and may occur in the Mojave
due to imprecise nature of the southeast boundary of the Mojave. Despite the
fact that 15 plant community types were eliminated from further evaluation,
the remaining 18 cover types contribute 92% of the Mojave area.

Table MOJ-3. Percent area
of each natural plant community type at each management status level in the Mojave
Desert Region. * indicates addition to the standard CNDDB classification.

CNDDB
Code

CNDDB
Community Name (Holland 1986)

CNDDB
Rank

Status
1 %

Status
2 %

Status
3 %

Status
4 %

Total
Mapped Distribution (km²)

Status
1+2 %

22000

Desert
Dunes-East

S2.2/3.2

88.2

0.2

8.1

3.6

675.9

88.4

22000

Desert
Dunes-West

S2.2/3.2

46.0

0.0

43.1

10.8

199.5

46.0

33100

Sonoran
Creosote Bush Scrub-Mojave

S4

88.6

0.0

4.3

7.0

778.6

88.6

34100

Mojave
Creosote Bush Scrub-East

S4

49.4

0.6

35.5

14.5

15,202.3

50.0

34100

Mojave
Creosote Bush Scrub-West

S4

16.6

0.6

54.2

25.1

27,269.1

17.2

34210

Mojave
Mixed Woody Scrub-East

S3.2

71.2

0.7

23.2

4.9

4,472.9

71.9

34210

Mojave
Mixed Woody Scrub-West

S3.2

49.6

3.8

29.0

17.6

4,969.8

53.4

34220

Mojave
Mixed Steppe-East

S2.2

74.0

0.0

1.6

24.4

527.2

74.0

34220

Mojave
Mixed Steppe-West

S2.2

96.6

0.0

0.7

2.7

116.5

96.6

34240

Mojave
Mixed Woody and Succulent Scrub-Mojave (only occurs in East)

S3.2

68.3

0.0

22.3

9.4

521.7

68.3

34300

Blackbush
Scrub-East

S3.2

56.3

0.9

38,8

4.0

385.1

57.2

34300

Blackbush
Scrub-West

S3.2

70.5

1.0

20.0

8.5

963.2

71.5

35210

Big
Sagebrush Scrub-East

S4

91.2

0.0

1.4

7.4

353.1

91.2

35210

Big
Sagebrush Scrub-West

S4

5.7

16.4

58.8

19.1

4.3

22.1

35213

Black
Sagebrush Scrub *

--

96.7

0.0

3.3

0.0

18.2

96.7

35400

Rabbitbrush
Scrub

S5

0.0

0.0

0.1

99.9

31.9

0.0

36110

Desert
Saltbush Scrub-East

S3.2

38.2

0.2

47.2

14.5

1,130.3

38.4

36110

Desert
Saltbush Scrub-West

S3.2

5.3

1.6

37.4

55.6

2,780.8

6.9

36120

Desert
Sink Scrub-East

S3.1

64.9

0.0

27.8

7.3

132.0

64.9

36120

Desert
Sink Scrub-West

S3.1

1.4

4.4

74.9

19.4

158.2

5.8

36130

Desert
Greasewood Scrub

S3.2

0.0

0.0

0.1

99.9

1.7

0.0

36140

Shadscale
Scrub-East

S3.2

93.5

0.0

6.2

0.4

1,762.1

93.5

36140

Shadscale
Scrub-West

S3.2

43.4

11.2

34.3

11.1

677.1

54.6

36150

Desert
Holly Scrub-East *

--

45.9

0.0

51.5

2.6

303.9

45.9

36150

Desert
Holly Scrub-West *

--

71.0

1.5

25.5

2.0

1,144.1

72.5

37200

Chamise
Chaparral

S4

0.0

0.0

35.4

64.6

57.0

0.0

37400

Semi-Desert
Chaparral-East

S3.2

0.0

0.0

64.5

35.5

0.9

0.0

37400

Semi-Desert
Chaparral-West

S3.2

8.3

0.1

20.0

71.7

450.6

8.4

37A00

Interior
Live Oak Chaparral

S3.3

0.0

0.0

51.8

48.2

113.7

0.0

42160

Desert
Native Grassland-East *

--

0.0

0.0

92.0

8.0

208.2

0.0

42160

Desert
Native Grassland-West *

--

0.0

1.7

41.0

57.3

92.1

1.7

42200

Non-Native
Grassland

S4

4.1

3.6

0.8

91.5

278.0

7.7

42300

Wildflower
Field

S2.2

0.0

0.0

31.5

68.5

7.0

0.0

46000

Alkali
Playa-East

S3.2

59.9

0.1

35.5

4.6

398.2

60.0

46000

Alkali
Playa-West

S3.2

1.4

4.4

75.0

19.2

889.2

5.8

52320

Transmontane
Alkali Marsh

S2.1

0.0

43.0

0.0

57.0

2.5

43.0

52420

Transmontane
Freshwater Marsh

S2.2

100.0

0.0

0.0

0.0

3.0

100.0

61610

Modoc-Great
Basin Cottonwood-Willow Riparian Forest

S2.1

52.2

12.4

7.0

28.4

2.0

64.6

61700

Mojave
Riparian Forest-East

S1.1

9.4

3.0

56.8

30.8

27.5

12.4

61700

Mojave
Riparian Forest-West

S1.1

0.0

18.5

5.0

76.5

31.3

18.5

61820

Mesquite
Bosque-East

S2.1

72.4

0.0

18.4

9.2

210.7

72.4

61820

Mesquite
Bosque-West

S2.1

0.0

43.9

2.6

53.5

18.3

43.9

62200

Desert
Dry Wash Woodland-East

S3.2

5.6

1.4

67.0

26.1

205.2

7.0

62200

Desert
Dry Wash Woodland-West

S3.2

83.4

0.0

5.3

11.2

94.1

83.4

63700

Mojave
Desert Wash Scrub

S3.2

0.0

0.0

44.6

55.4

2.0

0.0

63810

Tamarisk
Scrub

S4

4.6

6.3

39.2

50.0

52.1

10.9

71410

Foothill
Pine-Oak Woodland

S4

0.0

0.0

1.7

98.3

7.7

0.0

72200

Mojavean
Pinyon and Juniper Woodlands-East

S3.2/4

67.7

0.0

29.8

2.5

911.1

67.7

72200

Mojavean
Pinyon and Juniper Woodlands-West

S3.2/4

33.0

2.4

21.2

43.3

901.9

35.4

86400

Bristlecone
Pine Forest

S2.3

100.0

0.0

0.0

0.0

3.8

100.0

Region
Total - Natural Communities in Mojave

69,530
(94.0%)

Region
Total - Natural Communities in East Subregion

35,203
(97.7%)

Region
Total - Natural Communities in West Subregion

34,315
(90.4%)

Region
Total - All Lands in Mojave

36.3

2.4

39.4

22.0

73,981

38.7

Region
Total - All Lands in East Subregion

60.5

0.4

29.9

9.2

36,021

60.9

Region
Total - All Lands in West Subregion

13.4

4.2

48.4

34.0

37,950

17.6

Due to the floristic dissimilarity
between the eastern and western subregions, the 18 remaining cover types were
subdivided by the two floristic regions into two subtypes each, an eastern and
western subtype. One of the cover types only occurred in the eastern floristic
region ( Mojave Mixed Woody and Succulent Scrub). This gives a total of 35 natural
vegetation subtypes that were given conservation evaluation (shaded rows in
Table MOJ-3). Following is analysis of the distribution and conservation status
of each cover type:

Desert Dunes (22000) can
be found in association with Alkali Playas or as discrete landform features.
The dune associated vegetation may occur in mosaics with Mojave Creosote Bush
Scrub and Desert Saltbush Scrub. Desert Dunes also are well represented in status
1/2 management (79% in the region, 88% in the East and 46% in the West) and
is almost entirely in public ownership (95%).

Mojave Creosote Bush Scrub
(34100) is the most extensive cover type in the Mojave Desert region, covering
57% of the land surface. Over most of its mapped distribution (81%) it is the
only vegetation type in a map unit but it can occur in mosaics with urban and
agricultural cover types (5% of occurrence). It's combined status 1/2 management
(Table 7-2) is lower than the current regional level (31% for the type compared
to 39% for the region). When regionalized, Mojave Creosote Bush Scrub in the
western floristic subregion has only 17% status level 1 and 2 protection, while
50% of the type in the eastern subregion was protected. While the total protected
acreage is large, the pattern of management is highly fragmented between management
status 1 and 4 or status 3 and 4 due to the checkerboard pattern of land ownership.

Mojave Mixed Woody Scrub
(34210) covers 13% of the Mojave. It is found in mosaics with any of the upland
scrub or woodland cover types, except the halophytic saltbushes. Over 62% of
its area is managed at status 1 or 2, regionwide. In the western subregion it
has 53% status 1 and 2 protection (Table MOJ-2), much of which occurs in Joshua
Tree National Park. In the eastern subregion, the percentage of protection is
72%. Mapping for this cover type is of low reliability (Thomas 1996).

Mojave Mixed Steppe (34220),
Mojave Mixed Woody and Succulent Scrub (34240), Desert Holly Scrub (36150) and
Blackbush Scrub (34300) are similar in that they each contribute 1-2% to the
total Mojave cover and are well represented in status 1 or 2 management (67
to 78% regionally, 46 to 97% in subregions). Of this group, mapping is considered
reliable only for Desert Holly Scrub (Thomas 1996).

Big Sagebrush Scrub (35210)
occurs mostly in the northern Mojave, with some patches in the central and western
Mojave. Although it is well represented in status 1 and 2 management (90%),
its protection is fragmented in the central Mojave. A small amount of the cover
type (344 ha) occurs in the western floristic subregion. This type is also widespread
throughout the Great Basin.

Desert Saltbush Scrub (36110)
often intergrades at lower elevations with Alkali Playa and Desert Sink Scrub,
and at higher elevations it is often found in mosaics with Mojave Creosote Bush
Scrub, Desert Native Grassland or urban/agricultural cover. Sixteen percent
of the cover type is in status 1 or 2 management regionwide. In the western
floristic subregion, this drops to 7%, and that occurs in highly fragmented
patches with both status 3 and 4 managed lands. It was observed that a high
proportion of associated species in Desert Saltbush Scrub - West Region are
invasive exotics (Thomas 1996).

Desert Sink Scrub (36120),
found at the upper edges of Alkali Playa Vegetation, has 33% status 1/2 representation,
although this drops to 6% in the western floristic subregion. Both Alkali Playa
and Desert Sink Scrub occur in discrete patches due to their association with
the actual dry lake basins.

Shadscale Scrub (36140)
covers 3% of the Mojave and occurs mainly in the northern floristic region.
It can be found intergrading with Mojave Creosote Bush Scrub as well as Mojave
Mixed Woody Scrub, Blackbush Scrub, and Mojave Mixed Woody Steppe. A high proportion
is in status 1/2 management both for the entire region (83%) and for the west
and east floristic subregions (55 and 94% respectively). Mapping reliability
for this cover type is considered low (Thomas 1996).

Semi-Desert Chaparral (37400)
is found along the south-western borders of the Mojave. It has low representation
in status 1/2 (8%) and is mainly under private ownership (72%). It is often
found intergrading with Mojavean Pinyon and Juniper Woodlands and Mojave Mixed
Woody Scrub.

Desert Native Grassland
(42160) occurs in discrete patches in the Mojave (<1% of the total land area),
has very low representation in status 1 or 2 managed areas (0.5%), but does
have high representation on status 3 lands (76%). It can be found in mosaics
with Mojave Creosote Bush Scrub and Desert Saltbush Scrub. In the western floristic
subregion, it has low acreage in total protection, around 150 ha. In the eastern
floristic subregion, the cover type is entirely in status 3 or 4 management.

Alkali Playa Vegetation
(46000) occurs at the edges of closed basins throughout the desert at lower
elevations. Approximately 60 playas or playa complexes are mapped on the Mojave
vegetation coverage. Over the entire region Alkali Playa has 23% distribution
in status 1/2 management but only 6% in the western floristic subregion.

Mojave Riparian Forest
(61700) is found along the Mojave River with varying density from the Mojave
River Forks to downstream of Afton Canyon. It is also found in small patches
along Little Rock Wash and Big Rock Wash and along the Amargosa River. It's
total coverage is small (5,880 ha, 0.08% of the land area) and 16% is in status
1/2 management. Field observations of Mojave Riparian Forest revealed that tamarisk,
an invasive exotic, has often heavily invaded and degraded its quality (Thomas
1996).

Mesquite Bosque (61820),
a streamside thorn forest often found in association with Alkali Playas or Desert
Dunes, has an overall status 1/2 representation of 70%. Status 1/2 representation
in the western floristic subregion is 44% but the total acreage in protection
is only slightly more than 800 ha (all in status 2).

Desert Dry Wash Woodland
(62200) was mapped by BLM (Dorweiler 1997) over a small area in the southern
portion of the region. The type is well-represented in status 1/2 managed areas
(31% in the whole region) but this is unevenly distributed between subregions
(83% status 1/2 in the western subregion, only 7% in the east). This type is
more widespread in the Sonoran Desert region.

Mojavean Pinyon and Juniper
Woodlands (72200) cover 2% of the Mojave. It occurs along the western and southwestern
borders of the Mojave and in discrete patches in the interior. In the western
floristic region it occurs in mosaics with Semi-Desert Chaparral or Non-native
Grassland. In the interior of the region, the cover type can be found in mosaics
with Mojave Mixed Woody Scrub or Blackbush Scrub. For the entire Mojave it has
52% status 1/2 management. It has 35% status 1/2 management in the western floristic
region and 68% in the east.

Of the 10 cover types identified
as vulnerable in this analysis, five have been rated as very threatened by the
Natural Heritage Division (NHD) of California Department of Fish and Game (Alkali
Playa, Desert Sink Scrub, Mesquite Bosque, Mojave Riparian Forest), two as threatened
(Desert Saltbush Scrub, Semi-Desert Chaparral), one as not threatened (Mojave
Creosote Bush Scrub) and two with no rating (Desert Native Grassland, both subregions).
These types were selected as vulnerable based on GAP criteria which are largely
separate from those of the NHD. The NHD identified two additional cover types
as very threatened; however, both these cover types were not evaluated in this
gap analysis because they were mapped on less than 25 km². Gap analysis
has revealed Mojave Creosote Bush Scrub in the western region to be under-represented,
while it is rated as not threatened in the NHD ratings.

A special word should be
stated about Joshua Tree Woodland (73000). This type was not mapped as a specific
plant community type in the GAP land-cover database. The presence of Joshua
Tree (Yucca brevifolia) was recorded as a dominant or special interest
species where possible. Frequently, however, the density of Y. brevifolia
is so low (or unknown) that the community must be classified as a scrub
type. From the information in the GAP database, Joshua Tree occurs in approximately
15% of the Mojave, and it appears to be well represented in protected areas.
The Natural Heritage Division rates Joshua Tree Woodland as very threatened.
Due to the high uncertainty regarding Joshua Tree Woodland, we are unable to
evaluate its current management status reliably at this time.

We have not yet applied
formal siting models to identify priority areas in the Mojave Region. Based
on the gap analysis of plant community types, Thomas (1996) identified 7 areas
with high potential for improving representation of under-represented types
(Figure MOJ-1). Areas in the Mojave were selected that support vulnerable cover
type(s) that have one or more of the following characteristics: 1) a high (70%
or more) coverage of vulnerable cover types in map units occurring in the area,
or with vulnerable cover types occurring in adjacent map units, and 2) with
open space or unknown zoning, if on private land, or 3) some indication that
management changes could be facilitated if on federal land. Zoning designation
for Los Angeles and San Bernardino counties was provided by the Southern California
Association of Governments (SCAG) from their general plan (Crowe 1996). The
zoning categories in the SCAG general plans were aggregated into four zoning
categories: open space, urban developed, agriculture, and unknown. These 7 areas
are only suggested as areas for more detailed consideration in region wide conservation
planning in the Mojave.

The West Antelope Valley
site (Area A, Fig. 7-1) occurs at the base of Tehachapi Mountains in parts of
Winters Ridge, Liebre Twins and Willow Springs 7.5' topographic quads. Semi-Desert
Chaparral and Desert Native Grassland occur in this area. Land ownership is
predominantly private; zoning is unknown.

Another area supporting
Semi-Desert Chaparral is in a strip of land along the base of the San Gabriel
Mountains (Area B). This strip occurs east of Highway 14, south of Hwy. 138
and west of I15 and is contained in parts of Lancaster East, Pacifico Mountain,
Hi Vista, Valyermo, and Phelan 7.5' quads. Mojave Riparian Forest that occurs
around Lake Palmdale and Little Rock Wash occur also within the strip. Mojave
Riparian Forest occurring in Big Rock Wash is found downslope of the strip in
Hi Vista quad. Much of the land is privately owned, zoned for open space. Along
the southern border of the strip, some National Forest lands occur.

The area including and
surrounding the Rosamond, Buckthorn and Rogers Playa complex (Area C) supports
Mojave Creosote Bush Scrub - West Region, Desert Saltbush Scrub - West Region,
Desert Sink Scrub - West Region as well as Alkali Playa. This area is contained
within the Bissell and Rogers Lake North topographic quads. It is predominantly
administered by Edwards Air Force base under status 3 management.

The Koehn Lake area (Area
D), centered around a playa north of the Rosamond Playa complex contains the
same vulnerable cover types. Land ownership in the area includes status 1 managed
lands to the east, status 3 managed lands in and immediately adjacent to the
playa, and status 4 lands to the west. Koehn Lake is found in the Garlock quad.

A small, apparently unnamed,
playa (Area E) west of Hwy 395 in the Boron NE quad is surrounded by Desert
Saltbush Scrub. The land management in this area is fragmented with BLM status
1 and 3 management in a checkerboard pattern with private (status 4) lands.

Two other candidate areas
occur around Harper Lake and the Superior Lake complex (Areas F and G), both
Alkali Playas. Both support Desert Sink Scrub - West Region and Desert Saltbush
Scrub - West Region, as well as Alkali Playa. North, and adjacent to the Harper
Lake playa is Desert Native Grassland. Desert Native Grassland is also mapped
to the east of Superior playa complex on the Fort Irwin military reservation.
Status 1 BLM land in a checkerboard pattern with private land occurs between
the two playas. Status 3 BLM land fragmented with private land occurs around
each playa. Fort Irwin status 3 land occurs north of the Superior playa complex.